Whidbey Island has over a hundred miles of beaches that you can walk on but be very careful that you know the tides when you walk. Always walk on a outgoing tide or know when the high tide will occur. Many beaches have high bluffs and the water will leave no room to walk during high tides. Particularly if there is a storm the waves will crash against the bluffs making walking dangerous. There is plenty of clams and mussel digging on the eastern shores and beach combing on the western shores. If you like fresh dungeness crabs or shrimp bring a small rubber raft or boat. You can also get crab from the docks in Langley or Cornet Bay.
Sorry, but swiming around Whidbey's beaches are only for the strong at heart. The waters generally average from 48 to 52 degrees. Much to cold to swim in. It can warm up a little near the warm beach sand, for wading.
Some friends were ransacked by chipmunks and squirrels in South Whidbey State Park. They left their grocery bags out on the picnic table while they napped in their tent. These critters were surprisingly agressive. Do not feed them by your hand or you might get a rabbies bite.